The present invention relates to a unit for feeding and cutting into discrete lengths a strip of wrapping material.
The discrete lengths thus obtained are used in a machine for packaging commodities.
Units of the type in question are used typically to cut a continuous strip of metal foil paper into single leaves, which are then fed to the wrapping unit of a cigarette packer and folded each directly around a respective group of cigarettes to form an inner wrapper in the finished packet.
The leaves of metal foil paper are generated by making transverse cuts through the strip and appear rectangular in outline, the predominating dimension aligned on the axis of the strip. Each single leaf presents a corner area with two tear-off lines, one longitudinal, one transverse, combining to delimit a rectangular portion known as a “pull”, which can be removed by the user at the moment of breaking open the packet of cigarettes.
Conventionally, feeding and cutting devices used to generate the single leaves of material comprise a first roller and a second roller rotatable about mutually parallel axes in opposite directions, each of which is equipped with two diametrically opposed blades extending parallel to the axes of rotation.
The first roller has an aspirating cylindrical surface and, besides affording a reaction element in the course of the cutting step, serves also to advance the strip of metal foil paper decoiled from a relative roll, and to convey the leaves separated by the cutting action toward a further processing station.
The two blades of a first pair mounted one to the first roller and one to the second, substantially equal in length to the transverse dimension of the strip, serve to make the cut by which the leaf is separated from the strip. The blades of a second pair serve to impress the transverse tear-off line aforementioned.
Also forming a part of the feeding and cutting device is a disc cutter rotatable about an axis parallel to the axes of the two rollers, operating in combination with the first roller to impress the longitudinal tear-off line aforementioned.
In the conventional feeding and cutting devices thus briefly described, accordingly, the transverse tear-off line occupies an intermediate position, located between and at a set distance from the two shorter cut edges of the rectangular leaf.
It can happen, for example when changing from one type of metal foil strip to another, or changing the arrangement of the rows of cigarettes making up the group, or changing the brand of cigarettes in production, that the longer dimension presented by the removable part of the wrapper needs adjusting in order to avoid any incorrect alignment of the inner wrapper, and more particularly of the pull portion, relative to the group of cigarettes. This same adjustment serves also to avoid damaging the cigarettes through contact with folder mechanisms placed, in the case of the typical wrapping method, to engage the end portions of the flank faces when making the end folds of the inner wrapper.
The object of the present invention is to provide a unit for cutting a strip of wrapping material into discrete lengths such as will be unaffected by the aforementioned drawbacks.